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Eyes are very important as not only are they said to be the windows to the soul but they are often the points of highest contrast and thus draws the viewers' eyes to them. An important aspect of eyes are the specular highlights. For one thing, they give life to the eyes. Here is a demonstration and you can see the difference:

Apparently there was something known as "The Pixar Problem", as coined by my professor, and that is the incorrect placement of the specular on the eyes of the characters. As of to date, no Pixar movie has the eye spec in the correct place. The specular highlight of the eye should fall on the edge of the pupil. This can be simply researched by googling "eyes". The specular highlight falls in that exact place each and every single time due to the outward bulge shape of the cornea.

Without the bulge in the cornea, the specular highlight often goes up high on top but is occluded by the eyelid so it's not seen. Usually modelers would model the cornea of the eyes with the bulge and so everything works fine. Eyes are usually a small size and the slight bulge in the eye wouldn't be extremely apparent so it can be passed off. However issues may arise when you have characters like Mike from Monster's Inc where he is a large eye and building a bulge into the model would give off some creepy and unappealing results.

Thinking that it couldn't be done, having both an appealing eye and a correct specular, many animated movies have just gone along and went with the wrong specular on eyes. That is until Horton Hears a Who, by Blue Sky. They have specular with the correct placement on the eye and it doesn't bulge out awkwardly. Such an amazing accomplishment but there won't be a giant talk at SIGGRAPH and you won't hear about it in detail anywhere. This is not because it is some sort of super trade secret that no one else must know but because the solution is extremely simple and that it would make for a very boring lecture. The solution is to use a bump map. Yes, that is all, use a bump map. Use a black and white gradient with a circular ramp and plug that into the bump map channel and there you have it.